May 2001 meeting of SC-04-03

[Last printing 9 August 2001]
Report of the SC-04-03 Working Group on Loudspeaker Modeling and
Measurement of the
SC-04 Subcommittee on Acoustics meeting, held in conjunction with
the AES 110th Convention in Amsterdam, The Netherlands, 2001-05-14

Chair D. Prince convened the meeting. The agenda and the report from the
previous meeting were
approved as written.

No action was taken. The document was distributed and the chair requested
that members
review the document for the next meeting. J. Woodgate requested that
AES-1id
discussions
be kept independent from AES2.

AES2-R Revision of AES2-1984 (r1996) Specification of loudspeaker
components
used in professional audio and sound reinforcement

A report of SC-04-03-A meeting on 01-05-12 was given by Woodgate.
Considerable discussion ensued the chair feels stemmed from a
misunderstanding of
a certain terms, these notes intend to summarize the resolved discussions.
J. Brown requested clarification on impedance plots. The current intent
is that
the frequency axis be specified and the vertical axis have several ranges
in
linear format with a log scale allowed. Difficulty in covering large
ranges was
acknowledged. Brown desired to see a log axis. S. Temme noted that it is
hard to get a number off a log graph and preferred a linear scale.

W. Ahnert questioned the status of polar resolution and phase information.
Prince noted that the distributed PTD did not include the latest revisions
on polar
information. The WG will reference AES-5id and define a minimum
number of angles for measurement within the specified coverage angle.
AES2
could also reference material developed im project AES-X83 but does not
have a proposed document yet.

Prince asked for input from anyone interested in adding to the SC-04-03-A
work,
particularly on power compression.

A target date for a PWD was set for the 2001-09.

Woodgate encouraged manufacturers to use the PDF format rather than paper
for
issuing specifications..

B. Webb pointed out that many designers of simpler systems do not need
such
detailed information as suggested in discussions. Brown argued that he
does. Prince suggested that AES2 provide a detailed specification of
professional
speakers. If a smaller manufacturer targeting less complex systems does
not
comply with AES2, he felt that is the manufacturers decision and that it
is
up to
consultants and consumers to request compliance with AES2 if they need it.
D. Queen and Brown noted that the scope of AES2 was to define a minimum
data set for speaker designers to do their job.

At one point after some debate about the scope of AES2 Woodgate expressed
concern about members who only offer negative criticism. The AES2 PTD had
been on
the FTP site for some time and it appeared that some wanted to change the
scope late in the process.

Ahnert pointed out that the document has to work for the next twenty years
and needs to look forward.

Baird requested that AES-5id be referenced with respect to polar
resolution.

Prince reiterated that there are only three or four active members
contributing
to SC-04-03-A and those with further concern should get involved.

Prince noted also that the current use of small signal parameters and the
variations in measurement may warrant an annex or a separate information
document exhibiting the errors in method and the limitations of such
measures.

J. Stewart volunteered to see if a study of the different measurement
techniques was available at Harman.

Woodgate reiterated that the IEC document calls for vented box measurement
and
that measurement descriptions for the other methods have not been
forthcoming
for AES2 so he would attempt to describe them himself.

Hutt volunteered to see if D. Small would consider writing a summary on
the limitations of small signal measurement.

L. Fincham pointed out that these original authors readily acknowledge
that
it is a simplified model and only approximate in the linear range which is
easily exceeded in regular operation. He noted that the mechanical
parameters
are to be understood but not the derived.

Woodgate noted that he looks at a V-I figure on a scope in doing impedance
sweeps and rarely finds them to be well behaved but points out that it is
a
qualitative not quantitative measure.

Klippel points out that small-signal parameters have been in good use for
some time and just need to be extended. He thinks that large- and
small-signal parameters should be
examined together and not separately. Accordingly, the examination of
small
signal parameters could be added to the work in SC-04-03-C.

Status report from task group SC-04-03-B was presented. A technical
report is planned for 2001-09 in fulfillment of the project.

AES-X103 Large Signal Parameters of Low-Frequency Loudspeaker Drivers

A status report from task group SC-04-03-C was presented.
W. Klippel reported that work has been delayed. Prince requested that
discussions take place continuously on the e-mail reflector.

Klippel will summarize the current status and put information on the FTP
site and
reflector. A more complete report will be given in 2001-09.

New projects

Prince introduced the idea of a project to address the perception of
distortion
as the sound pressure level (SPL) increases, as raised at the
2000-09 meeting and in the work of other task groups within the SC-04-03
group. A. Voishvillo had begun a summary of distortion with respect to
multi-tone testing within SC-04-03.

S. Olive noted that he was hoping to pursue research as part of PhD work
starting this fall.

Discussion differentiating maximum SPL, frequently used for limits before
damage occurs to a speaker, and SPL without distortion ensued. Woodgate
pointed out that the maximum SPL measurement methods are defined already
within
IEC 60268-5 which is referenced by AES2. Webb noted the lack of
standards of current measures of maximum SPL.

Woodgate pointed out the difficulty in driver maximum SPL usage since it is
dependent on
loudspeaker design and construction. But it would be good to define the
standard so we at least know what was measured.

Brown pointed out that D. Cabot presented a paper recently on the subject.
S. Temme agreed to head up the investigation into this subject. A project
will
be initiated.

New Business

There was no new business.

The next meeting is scheduled to be held in conjunction with the AES 111th
Convention in New York, New York, US.